(a) Field of the Invention
The present invention relates to a method of controlling infeed in the so-called compound grinding for simultaneously grinding the inner and outer diameters of an annular workpiece, e.g., a bearing race on a single grinding machine.
(b) Description of the Prior Art
Generally, taking a bearing race as an example, the grinding of such annular workpiece is performed as follows.
First, the width surface of a workpiece having undergone pre-processes including lathing and heat-treatment is ground on a double head type surface grinding machine, followed by the grinding of the outer diameter on a centerless support type outer diameter grinding machine with said width surface as a reference, and then by the grinding of the inner diameter with said outer diameter as a reference. If the workpiece is particularly low in rigidity, the inner and outer diameters will be re-ground to maintain accuracy. Therefore, the processing of this kind of work requires a variety of grinding machines and a large installation space therefor, involving facility investment. It also requires transfer equipment such as chutes connecting grinding machines, and a large number of operators. In order to solve these problems, there has heretofore been a demand for developing a technique concerning the compound grinding of inner and outer diameters.
FIG. 1 illustrates a prior art embodiment of a compound grinding machine shown in U.S. Pat. No. 2,807,916 developed in response to such demand. As is clear from FIG. 1, this grinding machine comprises an outer diameter grinding device 1 and an inner diameter grinding device 2 which are arranged side by side, the arrangement being such as to solve the problems of said installation space, facility investment, transfer equipment and the number of operators. However, it has still been insufficient as to the shortening of cycle time, grinding accuracy, and adaptability to mass-production.
FIGS. 2 through 4 illustrate a compound grinding technique further advanced as compared with FIG. 1. In FIG. 2, the numeral 3 designates a spindle; 4 designates a driving plate attached to said spindle; 5 designates a workpiece; 6 designates an inner diameter grinding stone; and 7 designates an outer diameter grinding stone. The workpiece 5 is magnetically chucked to the driving plate 4 and, as shown in FIG. 3, it is centerless-supported as at 8a and 8b. The direction of rotation and the direction of infeed are as shown and the processing cycle is as shown in FIG. 4. In FIG. 4, (a) and (b) indicate cycles for the outer diameter grinding stone 7, (a) referring to infeed in the direction of X-axis and (b) referring to infeed in the direction of Y-axis. Further, (c) and (d) indicate cycles for the inner diameter grinding stone 6, (c) referring to infeed in the direction of Y-axis and (d) referring to infeed in the direction of X-axis. In this case, the workpiece 5 is a bearing inner race and the outer diameter grinding stone 7 is used to grind a rolling groove therein. Therefore, the Y-axis infeed (oscillation) of the outer diameter grinding stone 7 is not performed. The outer and inner diameter grinding stones 7 and 6 start infeeding at the same time. The outer diameter grinding stone 7 shifts continuously from rough grinding to precision grinding and, upon completion of operation, it sparks out for a fixed period of time and then returns rapidly. On the other hand, in the Y-axis infeed (traverse feed) (c) of the inner diameter grinding stone 6, oscillation is performed and in the X-axis infeed (d), rough grinding is performed simultaneously with rough grinding in (a). Immediately before completion of precision grinding by the outer diameter grinding stone 7, infeed (d) is once stopped and in infeed (d) the stone 6 is retracted to be subjected to dressing. Simultaneously with rapid return of the outer diameter grinding stone 7, oscillation is started in infeed (c), and in infeed (d) precision grinding is started. Upon completion of this precision grinding, spark out takes place, and rapid return takes place slightly earlier in infeed (d) than in infeed (c).
In the prior art, as described above, since precision grinding by the inner diameter grinding stone 6 is started simultaneously with the rapid return (with precision grinding completed) of the outer diameter grinding stone 7, the balance of the force exerted by the infeed of the inner diameter grinding stone 6 during that portion of the period of inner diameter grinding which requires the highest accuracy in such inner diameter grinding is upset, lifting the workpiece 5 at the shoe 8b (see FIG. 3), so that accurate support for the workpiece 5 can no longer be obtained, thus entailing the lowering of dimensional and configurational accuracy. To avoid this would involve the problem of prolonging the cycle time. That is, the compound grinding technique described above is a mere superposition of the conventional inner and outer diameter grinding cycles.